How does voice over wire or over internet work? How can we hear and understand another person in real time over such a distance via a digital transmission?

Question

Honest question I cannot wrap my mind around. How the hell does this work?

In: Physics

Answer 1

The big difference is how the sound is represented and digital transmission just adds another step in-between. In conventional analog transmission, the sound waves are air vibrations that cause a microphone to vibrate. The vibrating microphone generates a change in voltage and this signal is conveyed via a wire to a receiver. On the receiver’s end, the change in voltage vibrates a speaker which vibrates the air creating sound waves. Both the speaker and microphone are basically magnets attached to diaphragms and work according to electromagnetic induction.

Digital transmission adds a step in-between as the changes in voltage are converted, via an electronic device, into a different kind of analog signal that *describes* the original signal. The original analog signal will just be a series of high and low voltages that correspond precisely to the highs and lows of the original sound waves. The new signal will be a series of high and low voltages that represent numbers describing the highs and lows of the original signal. In its most basic form, an analog signal like this is represented as a series of numbers indicating the measured voltage at a particular time interval. This series of numbers is encoded into a signal using an agreed-upon convention and that signal is transmitted. On the receiving end, another electronic device takes this descriptive series of numbers and produces the proper voltages at the proper times corresponding to the highs and lows of the original analog signal.

The actual transmission is a bit more complicated, as sending and receiving a digital signal requires a standardized representation of the numbers as well as a method to coordinate the sending of the information (so that you know when one number ends and another starts). The information itself is typically compressed as a pure analog signal contains unnecessary information (e.g. sounds that cannot be heard) and takes up a large amount of bandwidth. There must also be methods to break this information up into easily-transmitted pieces with information on the source and destination. However, these methods and the infrastructure to support them are the same ones used for transmitting any other kind of data over a network and allows a single infrastructure to handle any kind of data to and from any device connected to the network.